A solution is prepared by dissolving 5.00g of an unknown molecular solid in water to make 500 ml of solution. The osmotic pressure of the solution is 1.61 atm at 25 degrees C. What is the molar mass of the solute?

This is what ive done so far:
M= 1.61atm/(0.0821Lxatm/molxK)(298K)= 0.0658mol/L